1. Field of the Invention
The present invention relates to a method for processing a digital image and particularly to a method and a system for digital image stabilization.
2. Description of Related Art
As technology advances, electronic products are developed to have more powerful functions. Besides multiple functions and practicality, electronic products are being miniaturized to meet the consumers' requirements. However, light and small-sized electronic products which have image capturing function are not easy to hold and easily result in image blurs.
Accordingly, the technology, image stabilization (IS), is developed to solve this problem. A digital image stabilization (DIS) system mainly includes a motion estimation (ME) unit and a motion correction (MC) unit. The ME unit is used for obtaining the local motion vectors of a plurality of areas in an image, so as to determine a global motion vector of the motion of the whole image. The MC unit is used for removing unnecessary blurs from the image based on the information obtained by the ME unit, and thereby produces stabile image output.
Mostly, the ME unit calculates the local motion vectors by a single bit-plane matching method or a multiple bit-plane matching method. Herein, the single bit-plane matching method carries out estimation merely based on the information of a certain frequency band in the image. Therefore, this method cannot provide favorable estimation of various images. Furthermore, when performing matching on an original image, this method consumes more time in binary bit-plane processing. The multiple bit-plane matching method simply analyzes an original bit-plane of the image, and two pixels having similar gray-scale values may result in different binary values in some original bit-planes, which reduces the accuracy of matching. In addition, a global motion estimation (GME) method performed by the ME unit is mainly to calculate the global motion vector based on all the local motion vectors. However, not all the local motion vectors indicate the actual motion directions. For this reason, the estimated global motion vector becomes inaccurate.
The aforementioned situations all bring negative influences to the digital image stabilization system, which not only impairs the accuracy of outputting stabile images but also complicates the hardware of the system.